figure



March 17, 1964 J. D. MEDLOCK ETAL ROCK BIT WITH REPLACEABLE AIR COURSE 4Sheets-Sheet 1 Filed May 22, 1961 52 JAMES D. MEDLOCK EDWARD M. GALLEFig. 5

INVENTORS GERALD O. ATKINSON March 17, 1964 J. D. MEDLOCK ETAL 3,125,175

ROCK BIT WITH REPLACEABLE AIR COURSE 4 Sheets-Sheet 2 Filed May 22, 1961lllIiIlI JAMES D. MEDLOCK EDWARD M. GALLE GERALD O. ATKINSON INVENTOR-TORNEY March 17, 1964 Filed May 22, 1961 J. D. MEDLOCK ETAL 3,125,175

ROCK BIT WITH REPLACEABLE AIR COURSE 4 Sheets-Sheet 3 Fig. 14

Fig. 15

Fig. 16

JAMES D. MEDLOCK EDWARD M. GALLE GERALD O. ATKINSON INVENT0R ATTORNEYMarch 17, 1964 J. D. MEDLOCK ETAL ROCK BIT WITH REPLACEABLE AIR COURSEFiled May 22, 1961 IIIIIIIILCQ? 4 Sheets-Sheet 4 JAMES D. MEDLOCK EDWARDM. GALLE GERLD O. ATKINSON 0R BYflZ WM) ATTORNEY United States Patent3,125,175 ROCK BIT WITH REPLACEABLE AIR COURSE Jamaal). Medlock, EdwardM. Gallo, and Gerald O. Atkinson, all of Houston, Tex., assignors toHughes Tool Company, Houston, Tex., a corporation of Delaware Filed May22, 1961, Ser. No. 111,518 12 Claims. (Q1. 175-337) The presentapplication is a continuation-in-part of copending application 88,160 ofthe same inventors, filed February ,9, 1961, and the benefit of suchfiling date is claimed for all disclosure therein which is common to thepresent application.

The present invention deals with rock bits of the rolling cutter type,and more particularly with those rock bits utilizing air or another gas,frequently laden with water or another liquid, as the flushing andcleaning medium. Such a bit is attached to a hollow drill string memberthrough which the gas is pumped to the bit and thereafter through anumber of passages in the bit to the bottom of the hole. Some of thesepassages divert part of the gas to the bearing spaces between therolling cutters and their associated shafts to cool these elements andto keep such spaces cleared of foreign matter and abrasion products, thebalance of the gas being passed directly through other passages in thebottom of the bit head to impinge either on the exterior of the cuttersor directly on the formation being drilled, or a combination of both.

In the prior art, it has been customary to provide one or more suchpassages at or near the bit axis for the direct air flow, such passagesbeing commonly known in the art as drilled air courses. When an airstream passes through such air courses at the flow rate necessary tocarry away the cuttings produced by the action of the bit, there isfrequently severe erosion of the cutter cutting structure.

Since a typical modern bit has three cones interfitting so closely as toleave no gaps except toward the bit periphery, such erosion could not beavoided by reorienting the centrally disposed air courses. Otherexpedients were adopted, e.g., moving the air courses to locations nearthe bit periphery in the gaps between the cutters, thus converting thestructure to what is now commonly called a jet bit. Jet bits do notpresent the same erosion problems, but they are more difiicult tomanufacture and consequently are more expensive than drilled air coursebits.

It is the primary purpose of the present invention to provide a rock bitof the rolling cutter type in which a gas may be passed axially andgenerally centrally from the cavity in the hollow bit head to the bottomof a formation borehole with little or no erosion of the rolling cuttersmounted below the head of such bit, but with adequate clean-up of theformation cuttings.

Another purpose is to provide such a bit in which portions of the gasstream are diverted into the bearing spaces between the rolling cuttersand their shafts, such gas thereby flushing and cooling the bearingsurfaces, and in which means are provided to prevent the introduction ofparticulate material with the gas passing into the bearings.

Another difficulty with the prior art drilled air courses relates tochangeovers in such air courses dictated by changes in drillingconditions and available equipment. When such changes require areduction in orifice size, a sleeve must be inserted in each hole, asimple but nevertheless somewhat time-consuming procedure. On the otherhand, when the orifice size must be increased, it is generally necessaryto ship the bit to a machine shop for re-working, i.e., reaming out theoriginal air course to a larger diameter.

It is a further object of the present invention to provide a bit havingthe previously mentioned advantages and also having the advantage ofreplaceability of that part of the bit defining the air course. Statedin diiferent words, that part of the bit through which air or other gasflows may be removed and replaced with a different but similar member tochange one or both of the flow rate of the gas and the pressure dropthrough the bit.

In arriving at the present invention, it was first determined that thecutter erosion characterizing prior art bits did not result from theintroduction of abrasive particles with the air entering the bit fromthe drill string, but rather was the result of turbulence in the airafter its passage through the bit. Such air leaves the bit and strikesthe rolling cutters and the bottom of the borehole with considerablevelocity. Cuttings and rock dust are picked up by this violent air andrecirculated with various turbulent trajectories in the spaces betweenthe cutters, bit head and borehole bottom before such air and its loadpass into the annulus around the bit and upwardly through the annulussurrounding the drill string. When such turbulent air collides with thehigh velocity air emerging from the drilled air courses of the bit, inthe space between the bottom of the bit head and the cutters, therecirculating rock cuttings and rock dust are violently projecteddownward on the top surfaces of the cutters. The action is similar tosand blasting, and the result is an accelerated wearing of the cuttingstructure, particularly toward the center. The elfect is most pronouncedwith the more abrasive formations.

Although prior art air bits were designed with the tacit assumption thatextremely high velocity air was required at the bottom of the borehole,the theory underlying the present invention discards such assumption andsubstitutes the idea that efiicient entrainment and asportation ofcuttings can be accomplished with lower velocity air. In comparing thebehavior of the bits of the present invention with that of prior artbits which satisfactorily accomplish the bottom flushing and cleaningfunction, the important criterion is to maintain about the same massflow rate.

Continuing such comparison, it seemed apparent that air bits of thepresent invention could be developed from the older drilled air coursebits simply by providing a single large air course at the axis, largerthan either a single prior art air course or the combined multiple aircourses in cross-sectional area. This would virtually eliminate anypressure drop through the bit and would make it possible to use a pumpof reduced pressure capacity while maintaining the same mass flow rate.

While a bit thus modified would be practicable with a sealed bearingbit, it could not be used to furnish the air for air-cleaned andlubricated bearings such as those employed with bits of the presentinvention. Experience with such air-cleaned and lubricated bearingsindicates that a minimum pressure drop over the bit of 15 psi. isrequired, and that 20 to 30 psi. or higher is preferable. To providesuch a pressure drop through the bearing structure, it is of coursenecessary to provide the same drop in the passageways used to supply airdirectly to the bottom of the hole.

It thus became apparent that the bits of the present invention shouldhave about the same pressure drop through the bit as those of the priorart, and should deliver volumes of air at about the same rate, but withlower linear velocities of the emerging gas stream at the axialpositions where such streams contact the cutter surfaces. It wasdetermined that this must be accomplished by causing rapid divergence ofthe central airstream at some point downstream from the high pressurearea where a portion is diverted to the bearing ports, and it isaccordingly an object of the present invention to provide a bit whichwill cause a rapid divergence of the central airstream. Such divergencemust be large compared with the substantially non-divergent emergentairstreams of prior art bits to avoid the abrasive wearingcharacteristic of prior art bits. Stated in other words, an object ofthe present invention is to provide a rock bit with one or more centralair flushing passageways in which there is considerably less abrasion ofthe cutting structure than with comparable prior art bits under the sameconditions.

The explanation below of the manner of accomplishing this object andthose mentioned above will be apparent to those skilled in the art froma consideration of the drawings attached hereto, in which:

FIGURE 1 is a partially sectioned elevation of a rock bit of the presentinvention complete with one cone, it being understood that there maybetwo, three or more similar cones, and that other types of rollingcutters including reamers may be used,

FIGURE 2 is a partial cross section on lines 2-2 of FIGURE 1, showing adetail of the ball loading bore and ball plug therein to illustrate theair passage therebetween,

FIGURE 3 is a partial section, similar to that of FIG- URE 1, of analternate embodiment which includes an alternate optional structure foravoiding the introduction of particulate material into the bearingports,

FIGURE 4 is another partial section like that of FIG- URE 3 showinganother optional alternate structure for keeping particles out of thebearings, and also an alternate nozzle shape,

FIGURE 5 is a partial section showing still another alternate screenstructure, together with alternate nozzle structures,

FIGURE 6 is a partial section of a bit head showing a means forretaining a nozzle in an unstepped head passage way, and also showing amodified form of exit orifice,

FIGURE 7 is a partial top view of the FIGURE 6 embodiment,

FIGURE 8 is similar to FIGURE 7 but with an axial groove cut into thebit pin rather than the nozzle,

FIGURE 9 is a partial section similar to FIGURE 6 but with a downstreamorifice formed in'the bit head,

FIGURE 10 illustrates a bit head with two orifices formed in a bit head,

FIGURE 11 illustrates a modified form of the invention utilizing threeseparate openings to define an upstream orifice,

FIGURES 12 and 13 show various forms of alternate exit orifices,

FIGURE 14 illustrates one way of shaping an upstream orifice,

FIGURES 15 and 16 show an alternative embodiment illustrating that theupstream orifice may not only be divided but also that it may be slantedwith respect to the bit axis, FIGURE 15 being a top view of the orificeand FIGURE 16 a section on lines 1616 thereof,

FIGURES 17 and 18 show an alternative embodiment in which the memberdefining the orifice is curved, FIG- URE 17 being a longitudinal sectionon lines 17-17 of FIGURE 18,

FIGURES 19 and 20 show two alternative means for disposing an upstreamorifice plate in the bit head, and

FIGURE 21 illustrates an embodiment of the present invention in whichnot only is a ditferent means provided for supplying and screening highpressure air to the bearing ports, but also a novel means is providedfor securing a replaceable nozzle member in the bit.

Turning to FIGURE 1, the rock bit indicated generally at 1 includes ahead 2 having an upwardly extend ing tapered pin or shank 3 forattachment to the corresponding box in the lower end of a drill stemmember such as a drill pipe, drill collar or sub (not shown).

Depending from head 2 are one or more downwardly extending legs 4, fromeach of which a shaft or hearing pin 5 extends generally inwardly. Suchbearing pin 5 is cylindrical and stepped to. provide a pilot pin 6, thesurfaces of which are especially treated to obtain wear resistantsurfaces.

Surroundingpilot pin 6 is a bushing 7 of wear resistant material, and athrust button 8 of similar material is disposed at the lower end of thepilot pin. Each of the members 7 and 8 is f'orcefitted into theindicated recesses in the cutter 13. A. roller bearing is provided byrollers 9 mounted in registering annular grooves 10 and 11 in bearingpin 5 and cutter 13, respectively, and a ballbearing is provided byballs 15 mounted in similar registering annular grooves. All of suchrecesses and grooves may be considered as enlarged parts of the hearinggap 14. The cutter is originally mounted with rollers 9 in place, afterwhich balls 15 are loaded through ball loading opening 16 to lock thecutter in place. The escape of balls 15 is avoided by inserting'ballplug 17 in opening 16 until the contoured end 19 is flush with thecorresponding groove in bearing pin 5, after which the position of ballplug 17 is secured by welding it to leg 4 with weld metal 18;

It should be noted that a flow passage is provided between balls 15 andthe portion of ball plug 17 underlying the downward terminus of fluidpassageway 25 extending from the main opening 2%) in pin 3. Such flowpassage is provided by the annular gap 28 surrounding reduced diameterportion 26 of ball plug 17 and the axially contiguous spaces 29 betweenball loading bore 16 and the wedge shaped portion 27 of ball plug 17(see FIG. 2). An alternate passageway which may be substituted or usedin addition is indicated by the dashed passageway 30. Many otheralternate passageways may be used to furnish air for the bearings. It isnot necessary to utilize opening 16, but the latter is convenientlyavailable.

It should also be noted that the various bearings mentioned above andthe various members defining such bearings are so proportioned as todefine gaps appropriate for the pressure drops mentioned above. This isentirely a matter of engineering experience, and is mentioned herelargely as a reminder to those of ordinary skill in the art seeking-tolearn how the present invention may be constructed and used. In generalsuch bearing gap widths and lengths are calculated for satisfactorycleaning and cooling at a minimum pressure drop of 15-30 p.s.i., and itis apparent that higher pressure drops are beneficial to such cleaningand cooling.

No cutting structure has been shownon the surface of cutter 13 becausethe present invention is not concerned with or limited to any particularcutting structure. It is to be understood that some such structure isprovided and that it may take many forms, e.g., integral teeth orinserted wear resistant compacts of the type introduced to the trade inrock bits now known by the Hughes Tool Company trademark Hugheset.

The number and shape of the cutters may vary, but typically there arethree conical cutters, as in the three cone bits sold to and known inthe trade under the Hughes Tool Company trademark Tri-Cone. Such conicalcutters are disposed uniformly around the bit axis and define a space 12lying above cutters 13 and below the bottom of bit head 2. It is intothis space that the major flow of air is discharged from the mainopening 20 of hollow pin 3.

Returning to FIGURE 1, itcan be seen that the bottom of bit head- 2 hasbeen machined out as a large center borewall 33, into which is insertedthe air course nozzle generally indicated as 40. This nozzle includes asmajor parts the cylindrical wall 41, upper orifice plate or transversemember 42 defining orifice 43, and flared bearing port screen or skirt44v provided with axial slots 45 to allow air to pass into gap 46between the bore 21 of the pin and nozzle 40, and thence through ports24 of fluid passageways 25. Slots 45 are sufiiciently narrow to preventall but very small particles from entering ports 24, e.g., A3 inch.

While the flared bearing port screen 44 is not indispensable, it doesprotect against the introduction of trash through bearing ports 24 inthe event that water or some other formation fluid rises through thenozzle, carrying with it cuttings or other comminuted material, as isparticularly likely to happen when the air supply is shut off.

When screen 44 is used, it need not necessarily be provided with slots45 around the complete periphery of the nozzle, as shown, but may belimited to one or more slots in the vicinity of each bearing port. Thenumber of slots is somewhat arbitrary, so long as a suflicient numberare provided to insure essentially a zero pressure drop from above thenozzle to gap 46, but the preferable construction is to space slots 45uniformly and frequently about the entire periphery of the upper edge ofthe nozzle. This construction makes it possible to use a nozzle having agreater outside diameter in its uninstalled position than the insidediameter of the bore 21 at the height of contact, thereby providing asmall force normal to such borewall which resists upward movement of thenozzle, normally not likely because it is held down by the downwardlyflowing air. For the same reasons, it is preferable to spring the websof material between gaps 45 in inserting the nozzle rather than makingthe maximum flare slightly less than the diameter of borewall 21 toprovide a filtering gap therebetween.

Nozzle 40 is secured against downward movement by a step or shoulder 47abutting against the corresponding corner of borewall 21. At and justabove such point, the nozzle wall 41 must be thick enough to withstandsubstantially the full pressure drop across the nozzle, from gap 46 tothe main opening 48 of the nozzle.

Near the bottom of bit head 2 a second transverse member is formed asnozzle wall 41 converges at surface 49, extends over a short straightportion 50 defining a Wide orifice 52 of only slightly smaller diameterthan that of the main opening 48, and finally diverges at surface 51.The relatively wide orifice converging-diverging nozzle thus formed isnot essential, and the nozzle may take the alternate form 40 indicatedin FIGURE 4, in which the main opening 48 does not change in cross-.sectional area at the lower end of the nozzle, or the alternate form 40of FIGURE 12, in which the main opening 48 flares divergingly at itslower end 52 at angle X. FIGURE 13 is similar to FIGURE 12 in definingan exit 52 of main passage 48 diverging at angle X, but utilizes theconstruction of FIGURE 5 in that exit orifice 52 is defined by the bithead rather than the nozzle, the bit passage 33 also being shouldered at53 to prevent downward axial movement of the nozzle.

FIGURE 3 illustrates an embodiment of the present invention in which thenozzle 40 does not include a flared bearing port screen similar toelement 44 of FIG- URE 1, but is similar in other respects. In thisembodiment, particulate materials may be prevented from en- .teringports 24- by as screen 35 secured in place by tack welding at 36 and 37.Screen 35 may be in short circumferential sectors, each covering asingle bearing port 24,

but is more conveniently a single cylindrical piece.

Although the structure of FIGURE 3 does not provide against upwardmovement of nozzle 40 it is ap parent that such movement may beprevented in many ways. The nozzle may be cemented in by adhesives, but

preferably is held by means permitting ready replaceability, e.g., asplit retaining ring engaging matching circumferential grooves inborewall 33 and the outside of nozzle wall 41.

FIGURE 4 is similar to FIGURE 3 except as mentioned above and exceptthat in FIGURE 4 a flat screen 38 is disposed on top of orifice plate42, and is secured in place by any suitable means such as tack welding39 securing it to borewall 21. Screen 38 may either com- 6 pletely fillthe cross-section of opening 20, as indicated, or may be annular,overlying only gap 46.

In the drawings, the cross hatching for nozzle 40 and its variantsindicates a synthetic plastic, and a wide range of thermosetting andthermoplastic resins may be used in forming the nozzle. Plastic piecesare preferred because they can be produced relatively inexpensively, butthere is no physical requirement barring the use of metals such as steeland aluminum, or other appropriate materials. The nozzle need only beable to retain its shape with pressures up to a maximum of the order ofp.s.i.g. and with a modest temperature rise, e.g., to 300 F.

It is believed to be apparent that the nozzles described above areeasily removeable through main opening 20 in pin 3. The FIGURE 4embodiment is somewhat of an exception when screen 38 is tack welded at39, but the use of such screen is not mandatory. Furthermore, suchscreen when used need not necessarily be secured to borewall 21, but maybe secured instead to the nozzle. Such removability is to be preferredto a structure in which the nozzle is more permanently secured in place,as by welding, because it is frequently necessary to make fieldchangeovers.

Many modifications of the nozzle structure shown are possible withoutdeparting from the basic innovation of disposing a flow restrictingorifice plate at a considerable distance upstream from a relatively widedischarge passage at the bottom of the bit head. The removable nozzlemay be terminated at some distance above the latter position, asindicated in FIGURE 5, a shoulder 53 being provided in the bit headpassage by making such passage step to a smaller bore 54, at the sametime providing for a flush fit between the bore of the removable pieceand the bore of the bit head. When the discharge orifice is to beslightly restricted, it may be so machined as a part of the bit headwhen the large pas sageway is formed, as indicated by the dashed outline55 thereof in FIGURE 5.

FIGURE 5 also illustrates an older form of bearing port screen 56 whichmay be used when desired. Screen 56 is essentially a tube having itsouter end closed and pierced with a number of flow holes 57.

In laboratory tests with the nozzle 40 exhausting into the atmosphere,the bore of main opening 48 was 2 orifice plate 42 was /8 inch thick,upper orifice 43 was 1 7 in diameter at an axial distance of 3%" fromthe lower end of the nozzle. At the lower orifice 52 cross sectionalangles with the axis of the nozzle were 45 for converging surface 49 and30 for diverging surface 51. The axial distances of these surfaces were4 for surface 49, /s" for surface 50 and l" for surface 51.

The diameter of lower orifice 52 was 2 inches.

The nozzle as thus constructed was tested with air at 30 p.s.i.g., theair containing suflicient water to render the discharge stream visible.The flow rate measured at the higher pressure was 815 cubic feet perminute (c.f.m.), and the included plane angle between the divergentextremities of the discharge was 26". Decreasing the distance betweenthe lower end of the nozzle and upstream orifice 43 to 2 /8" (slightlyless than the bore of passage 48) caused the discharge stream to narrowto an essentially straight, high velocity stream.

Such results were contrasted with those obtaining from prior art devicesby delivering the same type of air through a single drilled air coursethrough the bottom of the bit, i.e., by removing nozzle 40 from bit 1 ofFIGURE 1 and using a diameter of 1 for the entire length of borewall 33,approximately 2 inches. With the same 30 p.s.i.g. pressure drop over thebit, the upstream flow rate was 900 c.f.m. and the included plane angleof the discharge was only 7". The high velocity of the discharge was notsignificantly reduced up to 6 inches from the discharge exit bymodifying the straight through bore to provide a converging entrance, adiverging exit, or both.

Field tests were also run with the FIGURE 1 embodiment and with theprior art drilled air course bits, both drilling through the same levelsof the same medium hard iron ore formation and both otherwise identical9-inch (gage) bits which are sold and known to the trade as the HughesTool Companys W7R bits, as listed and described in its current catalogue23. Both bits were used with a pressure drop of 32-35 p.s.i.

In the FIGURE 1 embodiment, the replaceable nozzle was of syntheticplastic, had an upper orifice 43 of diameter, inch axial length, located3 above the bottom of the bit head, and a lower orifice 52 of 1 inchdiameter, A: inch axial length, located of an inch above the bottom ofthe bit head. The diameter of the main opening 48 was 1 This bit drilled1834 feet at 55 ft./hr., 6090 rpm. and 2040,000 lb. weight on bit,before dulling to the point of unprofitable drilling. Examination of thedull bit disclosed even wear over the cutting structure of each of thethree cones.

The standard prior art bit (W7R) had three /2 diameter holes of uniformsection drilled centrally through the bottom of the bit head on a %1"diameter bolt circle. This bit drilled only 557 feet at 53 ft./hr., atthe same weight and rotary speed, before dulling to the point ofunprofitable drilling. Examination disclosed that the teeth of the heelrows on each cutter were still capable of further drilling but that thecutting structures toward the center of all three cutters, including theentire spearpoint of the No. l cutter, had been completely eroded awayby blast effect. Similar comparative runs with the FIGURE 1 embodimentresulted in runs of 2333 feet and 2903 feet while the nearestcompetitive bit of other manufacturers made only 1215 feet.

In using the replaceable nozzle of the present invention, it may becomenecessary to provide for changes in flow rate, pressure or both. This ismost easily ac complished by replacing the entire nozzle with one inwhich the only important difference is the size of the upstream orifice.As an example, assume that a particular bit equipped with a nozzleprovided for a 32 p.s.i.

pressure drop and an air flow of 800 c.f.m. has been cleaning bottomsatisfactorily in a particular formation.

Witha change in formation, assume further that it becomes necessary ordesirable to increase the flow rate with the same pressure drop. This isprovided for by changing to a nozzle having a larger upstream orifice.If, on the other hand, the change is to be to a higher pressure at thesame flow rate (all flows being in volume under standard atmosphericconditions), the area of the upstream orifice must be decreased. Whenboth the flow rate and pressure drop are to be increased or decreasedtogether, a change may or may not be necessary, depending on therelative extent of the changes.

A number of generalizations have been deduced as a result of furtherexperiments with the FIGURE 1 embodiment and various modificationsthereof. The upstream orifice plate 42 should be located as far aboveexit orifice 52 as possible, at least as much as and preferably two ormore times the diameter of main opening 48. The bore of main opening 48should also be maximized. Apparently the initial gas stream emergingfrom the restricted upstream orifice 43 has a higher internal pressurethan the pressure of the gas in the main opening, and thus starts toexpand. When it can ex pand sufficiently to contact the borewall of themain opening, the area of contact progresses rapidly backward until thedischarge stream essentially fills the tube. Thus the greater the lengthof the main opening, the greater is the probability that the dischargestream will expand to make the initial contact.

While the diameter of the main opening 48 must be small enough to insuresuch initial contact, a large value is desirable because there is littlefurther divergence of the gas stream below the exit end or orifice ofthe main opening. The gas stream pressure at that point is about equalto the pressure of the surrounding gas, and there is no divergenceexcept by the frictional edge effect. The diverging exits of FIGURES 12and 13 capitalize on this effect, using values of angle X in the regionof /230 degrees, 15 apparently being better than either extreme.

As one example of the extent to which diffusion of the airstream can beaccomplished with a nozzle of the FIG- URE 1 type modified as in FIGURE12 with angle X equal to 15 and with a large length of main opening,such a nozzle had such length of 4%.", a main opening diameter of 1% andan upstream orifice diameter of 4;. With air delivered at a flow rate ofcu. ft. per minute at standard conditions and a pressure. drop of 20psi. over the nozzle, the included plane angle of divergence of theemergent air stream was 41.6". The nozzle thus described fits a rock bithaving a 4 /2-inch regular shank.

The further experiments mentioned above also verify that various otherembodiments utilizing variants of the single axial orifice are the fullequivalents thereof. Thus in FIGURE 11, showing a top. view of a nozzlesimilar to that in FIGURE 7, three openings 43 of 0.577" dia. wereprovided in a A" thick orifice plate 42, equally spaced on a 4" boltcircle. Tests therewith yielded the same results as with a singleorifice of the same area (1 dia.).

The thickness of orifice plate 42 is immaterial insofar as eifects ondivergence of the airstream are concerned. Like results were obtained onplates of from to 1 /2" thick. Of course, too thick a plate can resultin having the upstream orifice too close to the exit end of the mainopening, and will thus lose the advantage of an upstream location.

Shaping of the upstream orifice has no observable effect on thedivergence of the airstream leaving the nozzle, but it does increase theairflow over the unshaped orifice for the same pressure drop. Thus theentrance of the orifice 43 of the FIGURE 14 orifice plate 42 was roundedwith a radius half the thickness of the plate, and such eifects wereobserved. Itseems apparent that other shapes would cause like effects,e.g., the traditional elliptical design.

The orifice or orifices need not be coaxial with the bit axis, and thereis actually some increase in exit stream divergence observed therewith.Thus orifice plates similar to the orifice plate 42 of FIGURES 15 and 16contained three equally spaced /2" dia. openings 43 (in some cases dia.)inclined to the vertical but tangent to the bolt circle containing theircenters. The direction of slant was away from the direction of rotation,and angle Y was 20, 25 and 45 for different nozzles. Some increase indivergence was noted in each case over the divergence for the equivalentstraight through orifice. At thesame. time, little or no improvement wasnoted through the use of openings connecting gap 46 with main opening 48below the upper orifice plate, whether such openings were radial orinclined to the radial in either the same cross section, axially, orboth.

FIGURES 6 through 9 illustrate alternate means for securing thereplaceable nozzles 40 and 40 against axial movement. Some such means isnecessary in the FIGURE 6 embodiment because there is but one straightthrough opening 20 of bore 21 in'bit head 2, and pin 3, but it isapparent that the retaining means of FIGURES 6-8 can be used with theembodiments of FIGURES 1-5 previously described. In FIGURE 6 the upperpart of the nozzle is necked down to wall 59 to provide gap 46' aroundbearing ports 24, wall 5% extending above plate 42. A groove 60 isprovided in this upwardly extending part of wall 59, registering with asimilar groove 61 in borewall 21 of pin 3. A flexible split ringfastener 62 is seated in grooves 60 and 61 to prevent axial movement ineither direction.

An axial groove 63 is providedin the periphery of wall 59, extendingfrom the top surface to radial groove 60,

. 9 to permit the insertion of a compressive tool in assembly anddisassembly. Such a tool has points fitting into the indicated holes innibs 68 of the split ring (see FIG. 7), and is used to compress the ringand withdraw it from engagement in groove 61, the nozzle then beingremovable with the ring.

FIGURE 8 illustrates an alternate means for insertion of the compressivetool, through an axial slot 65 in the borewall 21 of pin 3, extendinginto radial slot or groove 61.

It is apparent that the nozzle 46 of FIGURE 6 may have an alternateupward termination which eliminates groove 60, as indicated by thedashed line 64 in FIGURE 6. With such construction, ring 62 preventsonly upward movement of the nozzle, and some means must be provided toprevent downward movement, e.g., the construction of FIGURE 9. Theconstruction of FIGURE 9 is the same as that of FIGURE 6 except that thelower orifice 52 is formed in a thin plate 58 extending from bit head 2.It is apparent that the restraint against downward movement of thenozzle provided by plate 58 can be retained when the lower orifice 52 isnot restricted by simply increasing bore 50 to a diameter less than thatof bore 33 but equal to or greater than that of the main opening 48 ofthe nozzle.

In the embodiments of FIGURES 6-9, air at the upstream pressure issupplied to the bearing ports 24 through a multiplicity of passages 66through wall 59. These passages are sufficiently spaced and sufficientlynumerous that they may be of relatively small size, e.g., inch diameter,and thus serve as the screen to prevent particulate material fromentering gap 46 and bearing ports 24.

FIGURE 10 has been included simply to demonstrate that the upstreamorifice plate 42 as well as the exit orifice plate 58 may be integralwith bit head 2. While such construction sacrifices the readyreplaceability of the earlier described embodiments, it does embody thebroadest inventive concept, that of a thin plate upstream orifice overwhich essentially the full pressure drop takes place. In thisembodiment, screen of the bearing air may be accomplished throughinserted screens 56, as described in connection with FIGURE 5, orequivalents.

FIGURES 17 and 18 depict a modification 40 of the nozzle 40 of FIGURE 1to illustrate that the orifice plate 42 may be curved and that orifices43 may be slanted at different angles spaced at various distances fromthe axis of the nozzle. Thus in FIGURE 18 the openings 43 aligned withthe vertical edges of the drawing are closer to the nozzle axis thanthose aligned with the horizontal edges. FIGURE 18 shows that suchopenings may be normal to the curved surface of plate 42 FIGURE 19illustrates a simplified form of orifice plate 42 which may be used toobtain the use of the maximum axial length of the bit. In thisembodiment the entire nozzle is reduced to such orifice plate 42containing orifice 43, the same being retained in borewall 21 of pin 3by the threaded engagement illustrated or by equivalent means such asthe split retaining ring of FIGURES 6-9. In this embodiment air to thebearings flows through a multiplicity of passages 25 passing through thewall of pin 3 to the top thereof. This is possible because there isactually a gap between the top of pin 3 and the lowermost surface of thedrill string member into which hit 1 is threaded. A multiplicity ofbearing air passages 25 converging in the lower portions of bit head areprovided to avoid weakening of bit head 2 that would occur with asingle, large bore air passage for each cutter. Such passages 25 aresufficiently small that no further filtering is necessary.

FIGURE 20 is a modification of FIGURE 19 illustrating an embodimentwhich avoids the likelihood of plugging the bearing air passages by thecollection of grease and dust. In FIGURE 20 the orifice plate 42 is setfurther into borewall 21 of pin 3, and an enlarged bore 22 may beprovided at the top of opening 20. A multiplicity of passages 25 areprovided opening through borewall 22 rather than through the top 7surface of pin 3, such passages 25 being similar to passages 25 innumber and diameter. Where necessary, they are jointed, or doubledrilled, as indicated.

FIGURE 21 illustrates still another embodiment of the invention,utilizing a nozzle 46 in which the orifice plate 4'2 and orifice 43 aredisposed at the maximum axial length above the discharge opening 52 atthe bottom of the bit head and the nozzle is retained in the bit by yetanother means. In this embodiment nozzle 40 is shaped to define gap 46communicating with bearing ports 24, wall 41 being of smaller outsidediameter than the outer diameters of orifice plate 42 and bottom flange23, the latter being essentially equal to that of borewall 21 of pin 3.Gap 46 extends upwardly to orifice plate 42, the air passage through theplate is provided by a multiplicity of passages 45 of sufficiently smallbore as to be self filtering. Alternately, passages 45 may be omittedand gap 46 may be connected to the air supply by passages 25 through thepin 3, or a combination of both may be used.

Nozzle 40 is held in position within pin 3 by a pair of radiallyextending retaining pins 32 extending through appropriate registeringopenings in bit head 3 and nozzle 42.. It is apparent, of course, thatother means such as the split retaining ring of FIGURES 6-9 may be used.The FIGURE 21 embodiment has the virtue that the replaceable nozzle neednot extend to the bottom of the bit head.

It will be apparent from the above that the upstream orifice need not beexactly coaxial with the bit, but on the other hand may departconsiderably from such condition. Broadly the invention comprisesproviding a main longitudinal opening of considerable diameter throughthe head of a rock bit and generally at the center thereof, anddisposing a member defining a relatively small orifice in such mainopening as far above the downstream terminus of the latter as possible.The upstream orifice-defining member should be so disposed as to allowaccess of the upstream gas to the bearing ports of the bit atessentially its maximum pressure, and the orifice of such member shouldhave a maximum cross-sectional area such that the pressure drop throughthe orifice is equal to or greater than the minimum pressure required tocool and clean the bearings.

What is claimed is:

1. A rolling cutter rock bit suitable for use with gaseous fiushingmedia comprising a head section with an upstandmg shank suitable forconnection to a drill string, said head and shank having an axiallyextending and coextensive central passageway therethrough, at least oneleg extending downwardly from said head, a bearing pin thereon extendinggenerally inwardly beneath said passageway, a rolling cutter rotatablymounted on said hearing pin to define therewith a hearing gap, passagemeans in said head, leg and bearing pin extending from said bearmg gapto a bearing port in said central passageway, and a member extendingtransverse said passagewy upstream from the exit end thereof, saidmember having at least one restricted orifice therethrough and beingsupported from the wall of said passageway to divide the passageway intoa high pressure zone and a low pressure zone, said low pressure zonelying downstream from said member and above the exit end of thepassageway, said member being secured to said wall against at leastdownward movement with respect thereto and to prevent the flow offlushing fluid into said low pressure zone except through said orifice,said bearing port being in communication with said high pressure zone,said passageway over the axial extent of said low pressure zone having aclear transverse cross-section generally at least as large as suchcross-section immediately below said transverse member.

2. The rolling cutter rock bit of claim 1 in which said clear transversecross-section diverges axially downwardly at the exit end of saidpassageway.

1 1 3. The rolling cutter rock bit of claim 2 in which said. cleartransverse cross-section diverges axially downwardly at the exit of saidcentral passageway at an angle of from 7 /2 to 30 degrees with the axisof the bit.

4. The rolling cutter rock bit of claim 3 in which said angle is about15 degrees.

5. The rolling cutter rock bit of claim 1 in which said transversemember is a part of a removable nozzle slidably and sealingly insertedinto said central passageway, said nozzle comprising a tubular wall andsaid transverse member secured thereto to block the flow of flushingfluid except through the orifice of the member, and said passageway wallis stepped inwardly to a smaller crosssection near its exit end todefine an upwardly facing shoulder, the lower end of said nozzle buttingagainst such shoulder in essentially flush relationship.

6. The rolling cutter rock bit of claim 5 in which the exit end of saidpassageway diverges outwardly and downwardly.

7. The rolling cutter rock bit of claim 1 in which said transversemember is a part of a removable nozzle slidably and sealinglyinserted-into said central passageway, said nozzle comprising a tubularwall and said transverse member secured thereto to block the flow offlushing fluid except through the orifice of the member, said tubularwall extending substantially to the exit end of the passageway andterminating in a downwardly and outwardly diverging opening.

8'. The rolling cutter rock bit' of claim 7 in which said nozzle wallterminates downwardly with an opening diverging at an angle of from 7%.to 30 degrees with the axis of the bit.

9. The rolling cutter rock bit of claim 8 in which said angle is about15 degrees.

10. The rolling cutter rock bit of claim 1 in which said transversemember is arcuate.

' serted in said central passageway from the top thereof and secured tothe wall thereof, said nozzle comprising a tubular wall and saidtransverse member, said wall being externally recessed to define upperand lower outside flanges slidably and sealingly engaging the wall ofthe passageway and a gap intermediate said flanges in communication withsaid bearing port, said transverse member being secured to said wall atabout said upper flange to block the flow of flushing fluid through theopening in the wall except through the orifice of the member, said upperflange having a multiplicity of self-filtering small passagescommunicating between said gap and the space above said shank.

References Cited in the file of this patent UNITED STATES PATENTS1,816,203 Behnke July 28, 1931 2,329,745 Crook Sept. 21, 1943 2,661,932Woods Dec. 8, 1953 2,719,026 V Boice Sept. 27, 1955 2,751,196 Smith-June 19, 1956 2,814,464 Pike et a1 Nov. 26, 1957 2,815,936 Peter et a1Dec. 10, 1957 2,880,970 SWart Apr. 7, 1959 FOREIGN PATENTS 763,676 GreatBritain Dec. 12, 1956 1,196,450 France May 25, 1959

1. A ROLLING CUTTER ROCK BIT SUITABLE FOR USE WITH GASEOUS FLUSHINGMEDIA COMPRISING A HEAD SECTION WITH AN UPSTANDING SHANK SUITABLE FORCONNECTION TO A DRILL STRING, SAID HEAD AND SHANK HAVING AN AXIALLYEXTENDING AND COEXTENSIVE CENTRAL PASSAGEWAY THERETHROUGH, AT LEAST ONELEG EXTENDING DOWNWARDLY FROM SAID HEAD, A BEARING PIN THEREON EXTENDINGGENERALLY INWARDLY BENEATH SAID PASSAGEWAY, A ROLLING CUTTER ROTATABLYMOUNTED ON SAID BEARING PIN TO DEFINE THEREWITH A BEARING GAP, PASSAGEMEANS IN SAID HEAD, LEG AND BEARING PIN EXTENDING FROM SAID BEARING GAPTO A BEARING PORT IN SAID CENTRAL PASSAGEWAY, AND A MEMBER EXTENDINGTRANSVERSE SAID PASSAGEWAY UPSTREAM FROM THE EXIT END THEREOF, SAIDMEMBER HAVING AT LEAST ONE RESTRICTED ORIFICE THERETHROUGH AND BEINGSUPPORTED FROM THE WALL OF SAID PASSAGEWAY TO DIVIDE THE PASSAGEWAY INTOA HIGH PRESSURE ZONE AND A LOW PRESSURE ZONE, SAID LOW PRESSURE ZONELYING DOWNSTREAM FROM SAID MEMBER AND ABOVE THE EXIT END OF THEPASSAGEWAY, SAID MEMBER BEING SECURED TO SAID WALL AGAINST AT LEASTDOWNWARD MOVEMENT WITH RESPECT THERETO AND TO PREVENT THE FLOW OFFLUSHING FLUID INTO SAID LOW PRESSURE ZONE EXCEPT THROUGH SAID ORIFICE,SAID BEARING PORT BEING IN COMMUNICATION WITH SAID HIGH PRESSURE ZONE,SAID PASSAGEWAY OVER THE AXIAL EXTENT OF SAID LOW PRESSURE ZONE HAVING ACLEAR TRANSVERSE CROSS-SECTION GENERALLY AT LEAST AS LARGE AS SUCHCROSS-SECTION IMMEDIATELY BELOW SAID TRANSVERSE MEMBER.